In what has a closed space having glass windows such as buildings and vehicles, generally, the glass surface is heated by solar radiation to become high temperature and the solar-radiation heat absorbed by the glass is radiated into the inside of a closed space such as the inside of a room or in the car to increase the internal temperature, which may cause various problems such that the effectiveness of an air conditioner comes down, especially in summer.
In order to prevent radiation of such solar-radiation heat, various glasses such as a heat wire absorbing glass which can absorb solar radiation and a heat wire reflection glass which can reflect solar radiation using various inorganic substances or organic substances have conventionally been developed.
However, these glasses are employing organic substances or inorganic substances which absorb solar-radiation heat as such, or metallic materials or inorganic substances which reflect solar-radiation heat as such so that the solar-radiation heat which penetrates the glasses and comes directly into the closed space can be intercepted.
In the glasses which can directly absorb or reflect the solar-radiation heat such as said heat wire absorbing glass and said heat wire reflection glass, a method increasing the amount of the substances which can absorb or reflect the solar-radiation heat directly may be available in order to improve the effectiveness of intercepting the solar-radiation heat. However, said method is accompanied by disadvantages in respect of practical use such that the cost becomes high and that the transparency of the glasses in a visible light zone decreases greatly and the inside becomes dark in result.
Moreover, there is a defect that a significant reduction of a thermal load of the inside of a closed space can not be counted upon, since the glass which has absorbed solar-radiation heat will radiate the heat absorbed by the glass again into the inside of a closed space gradually.
On the other hand, the glass which can reflect the solar-radiation heat does not become the cause of reradiation, since said glass hardly absorbs the light energy having the wavelength within the wavelength band of heat radiation at ordinary temperature. However, since it also uses metal, ceramics and the like which reflects an infrared light, it has such defect that it reflects even a visible light and consequently the inside of a closed space becomes dark.
In order to solve these problems, several ideas has been proposed such as a multilayer thermal insulating material wherein infrared radiation is reflected by sticking on a glass substrate a coating film whose visible light transparency is raised to about 70% by placing a metal layer in the middle and applying metallic cover layers on the both sides to adjust its refractive index (JP, 59-103749, A) and a low-emissivity glass wherein an SnO2:F film is used as a low-emissivity film to reduce radiation and an SnO2 film to an SiO2 film are laminated between a glass substrate and said Sn2:F film to reduce the generation of nonuniformity of color and a glass article using the same (JP, 2001-2449, A). However, the transparency of a visible light zone is still not enough.
Moreover, in order to prepare these glasses and films, it is necessary to use devices such as a vacuum deposition device and a sputtering device to coat metal or ceramics with the glass, which is largely disadvantageous, especially from an economical viewpoint.
From the above reasons, the development of an inexpensive heat-radiation-preventive glass which has high transparency at a visible light zone and is able to prevent heat radiation from the glass which has absorbed solar-radiation heat so as to reduce a thermal load caused by solar radiation has been waited for.
In light of the above problems, the inventors had found out that it is possible to prevent the heat radiation within the wavelength band of heat radiation at ordinary temperature from the glass which has absorbed solar radiation and has become high temperature effectively and to reduce a thermal load of the inside of a closed space, by forming a coating film wherein its visible light transparency is large and solar-radiation heat absorptivity and radiation heat absorptivity within the wavelength band of heat radiation at ordinary temperature are small on one side of a glass substrate, and disposing the glass so that said coating film side faces the inside of a closed space such as the inside of a room or in the car.
However, it is not necessarily easy to form a coating film having such capability of preventing heat radiation onto a glass substrate. That is, in order to apply the coating film onto window glasses of houses, window glasses of vehicles and the like, methods such as sticking on a glass by heat welding or adhesion a coating film which has previously formed in the shape of a film or a sheet, or a film or a sheet on which the coating film has been formed, coating plastics solved in a suitable solvent on a glass and then desiccating and solidifying or anchoring and the like are usually taken.
However, these methods have various defects such that they may require a large-scale equipment, that they may require a recovery treatment of a solvent which has been used for solving plastics when organic solvent-soluble type plastics is used, that it takes long time for desiccating and that the generation of unevenness of coating may often occur when a window glass having a coating film is produced by applying a coating film on the existing glass afterwards using water-soluble plastics.
Therefore, it had been difficult to stick a coating film on a glass without using films or sheets formed by uniformly coating onto various films by coater etc. Moreover, it had required specialized operators to stick these films and sheets on a window glass, which had been economically disadvantageous.
Therefore, development of an effective method for applying a heat-radiation-preventive coating film which is excellent in adhesion and durability onto the surface of one side of a glass uniformly, simply and economically had been waited for.